1. Field of the Invention
This invention relates to silver halide elements and more specifically to silver halide elements used to prepare half-tone images therefrom. Still more specifically, this invention relates to a novel group of hydrazines that can be advantageously added to said silver halide elements to improve the contrast and dot quality of images produces thereon.
2. Discussion of the Prior Art
Prior art silver halide elements used for half-tone work in the graphic arts industry, for example, usually employ standard silver halide elements that are processed in high pH developers that use hydroquinone or substituted hydroquinone as the main developing agent. These elements produce high quality images with excellent half-tone dots and high contrast. However, these processes are relatively slow and usually require an induction period before the so-called "lith" effect occurs.
Recently, there has been a pressing need in the industry to decrease the processing time required to product the lith images. Commercially, large users of lith products have demanded that the industry produce rapid-access products similar to that of the medical X-ray industry, for example. A number of prior art references describe the addition of various hydrazines to the emulsions or to the developers to obtain this rapid-access quality. Most of these references employ phenylformylhydrazine, or derivatives thereof, in order to achieve the requisite processability. However, the images obtained with these compounds is not as good as that which is achieved by normal lith products and the pH of the developers employed is still rather high.
Ruger, U.S. Pat. No. 4,937,160, Jun. 26, 1990, describes a system which uses a novel group of aryl hydrazides to achieve the rapid access processability at a lower pH. Good images and contrast are produced by the Ruger process. However, there is an ever increasing need to improve the images and dot quality even further.
It is an object of this invention to provide a silver halide element which can be processed under the conditions of rapid access and still produce a high contrast, high quality image with excellent dot quality. It is also an object of this invention to produce a silver halide element that can be processed at a lower pH than conventional, prior art elements, and yet produce an image with lower fog.